Nokia has revealed a limited duration of the battery to the software problem Lumia 800
only for the Cyan and Magenta.
As of January 18 there will be a sw update that will also apply directly to the end customer.

Meanwhile, if the customer insists on the immediate solution of the problem
proceed as follows: Open a SAT warranty notes indicating “Battery Problem”The terminal will be replaced with a new terminal

So an update is coming in around 2-3 weeks, and replacements will be given for those who cant wait that long.

You can check your battery capacity by typing # # 634 # and selecting “Battery Status”. If it reads 979 mAh or similar then you will be needing the update.

Remember dates should always be taken with a pinch of salt! But hopefully January will be the day that we all see better battery life from our shiny King!